1. Field of the Invention
The present invention relates to an X-Y input apparatus, and more particularly to an X-Y input apparatus suitable for use as a graphics input device associated with a graphic display apparatus.
2. Description of the Related Art
Graphic display apparatus are basically composed of a display screen, a display controller, a data channel, and an input device which may be in various forms. One known input device is a "joystic" (registered trademark) having a lever supported by a gimbal mechanism and tiltable by the operator in any direction of a plane. Detection is made of the direction and angle of tilt of the lever and then voltages or digital signals indicative of coordinate values in X and Y directions. This type of input device is disadvantageous however in that the range of angular movement of the lever is limited and input signals entered by the operator are relatively unstable.
In an effort to eliminate the above drawbacks, there has been developed an input apparatus called as a "mouse". One type of the mouse has a rotatable member such as a steel ball (hereinafter simply referred to as a "ball"), a first driven roller member held in contact with the ball and rotatable in response to rotation thereof, and a second driven foller member held in contact with the ball and rotatable in response to rotation thereof. The first and second rollers have their axes of rotation extending substantially perpendicularly to each other. The mouse also includes first and second angle detector means composed of variable resistors or encoders for separately detecting angles of rotation of the first and second driven roller members. The ball, first and second driven roller members, and first and second angle detector means are all housed in a casing.
The casing has an opening defined in its bottom with the ball partly projecting through the opening. In use, the casing is held by the operator to place the ball against a given base. By moving the case to cause the ball to roll on the surface in any arbitrary direction, the first and second driven roller members are rotated in their predetermined directions. The directions and angles of rotation of the driven roller members are converted by the first and second angle detector means into voltages or digital signals representative of coordinate values in X and Y directions. The generated signals are then entered into a display apparatus. The mouse is arranged in the above-described system.
In the conventional X-Y input apparatus, as previously described in detail, the opening is formed on the lower surface of the casing. The ball partially projects via this opening toward the lower direction. Then, the ball is rotated on the base while the casing is held by the operator, and the amount of the rotations of the ball is detected so as to input the data signals in the coordinate system. If contamination such as dust remains on the base, this contamination is attached to the ball, and then transported to the driven roller members in accordance with the rotating operations of the ball. In this case, if the touching planes of the driven roller members with the ball are formed in parallel with thier rotating axes, the contamination which has been transported to the driven roller members is deposited thereon, resulting in deterioration of detecting precision. This is because the surface of the ball is covered with an elastic material, so that the surface of the ball is slightly deformed to enlarge the contact area thereof which is in contact with the driven roller members while rotating the ball.